Implement receipt requirement threshold validation
epic-travel-expense-registration-core-services-task-002 — Add receipt attachment validation to the expense validation service. When total expense amount exceeds the configurable threshold (default 100 NOK per HLF requirements), the service must reject submission unless a receipt reference is present. Read the threshold from ExpenseThresholdConfig and return a structured validation error indicating the missing receipt.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 1 - 540 tasks
Can start after Tier 0 completes
Implementation Notes
Implement as a private method `_validateReceiptRequirement(ExpenseDraft draft, ExpenseThresholdConfig config)` returning `MissingReceipt?`. Keep it a pure function with no side effects. ExpenseThresholdConfig should be injected via Riverpod Provider so tests can override it. Use a sealed class or freezed union for ValidationError types to guarantee exhaustive handling in the UI layer.
Avoid using dynamic or Object as the error type. The threshold comparison should use integer øre arithmetic (multiply NOK by 100) to avoid floating-point precision issues when comparing e.g. 99.999 NOK.
Testing Requirements
Unit tests using flutter_test. Cover: (1) amount below threshold, no receipt → valid; (2) amount above threshold, no receipt → MissingReceipt error; (3) amount above threshold, receipt present → valid; (4) amount exactly at threshold → valid (inclusive lower bound); (5) threshold loaded from config, not hardcoded; (6) null receipt_reference treated same as empty string. No integration or e2e tests needed for this pure logic unit.
Mutual exclusion rules are stored in the expense type catalogue's exclusive_groups field. If the catalogue schema or group definitions differ between HLF and Blindeforbundet, the validation service must handle multiple group configurations without hardcoding organisation-specific logic.
Mitigation & Contingency
Mitigation: Design the validation service to be purely data-driven: it reads exclusive_groups from the cached catalogue and enforces whichever groups are defined, with no hardcoded organisation names. Write parameterised unit tests covering at least 4 different catalogue configurations to verify generality.
Contingency: If an organisation requires non-standard exclusion semantics (e.g. partial exclusion within a group), introduce an exclusion_type field to the catalogue schema and extend the service, treating it as a catalogue configuration change rather than a code fork.
The attestation service subscribes to Supabase Realtime for live queue updates. On mobile, Realtime WebSocket connections can be dropped during network transitions, causing the coordinator queue to become stale without the user being aware.
Mitigation & Contingency
Mitigation: Implement connection lifecycle management: reconnect on network-change events, show a 'reconnecting' indicator when the subscription is broken, and perform a full queue refresh on reconnect rather than relying solely on delta events.
Contingency: Add a manual pull-to-refresh gesture on the attestation queue screen as a guaranteed fallback. If Realtime proves unreliable in production, switch to periodic polling (30-second interval) as a degraded but functional mode.
If a peer mentor submits a draft while offline and then submits the same claim again after connectivity is restored (thinking the first attempt failed), duplicate claims may be persisted in Supabase.
Mitigation & Contingency
Mitigation: Assign a client-generated idempotency key (UUID) to each draft at creation time. The submission service sends this key as an upsert key to Supabase, preventing duplicate inserts. The draft is marked 'submitted' locally after first successful upload.
Contingency: Implement a server-side duplicate detection trigger on the expense_claims table checking (activity_id, claimant_id, created_date) within a 24-hour window and returning the existing record ID rather than inserting a duplicate.